Internal combustion engine
An internal combustion engine is an engine in which combustion, or the burning of fuel, occurs on the inside. It is a machine that makes small explosions inside a sealed box (cylinder). The explosions push a rod which is attached to a wheel. The pushing makes the wheel spin around. The spinning wheel is attached to other wheels, such as four car wheels, with a belt or a chain. The engine is very strong and can make all the wheels move. Engines need oil to make them slippery or the moving parts would grind together and stick. Parts of a car engine are measured to 0.01 of a millimeter and some engine parts fit together very, very tightly.
Most road vehicles use the internal combustion engine today, and most of those use the four-stroke engine. Rockets that go into space are combustion engines but they do not have wheels inside. The fire in a rocket combustion engine is so strong that it blows the rocket the same as blowing a piece of paper.
Another type of internal combustion engine is the Wankel engine.